Preparation of surfaces for coating



UNITED STA ES Patented May 31, 1932 PATENT OFFICE 'ELHIER M. JHIlNIIS, F DETROIT, MICHIGAN, ASSIGNOR IO PARKER RUST-PROOF COM- IPANY, OF DETROIT, MICHIGAN, A CORPORATION OF MICHIGAN No Drawing.

I PREPARATION or. sonmcns roe comma This invention relates to the preparation of surfaces for coating and more particularly 7 for coating with a layer of insoluble phos phatesformed in situ.

The invention consists in the electrolytic deposition of iron on a surface, and the subjection of the surface thus produced to a dilute solution of phosphates until a coating of insoluble phosphates is produced thereon;

The electrolytic deposition of iron may be accomplished in any well "known manner.

- For example, the article to be coated may be used as the cathode in a solution of ferrous ammonium sulphate. Preferably, a saturated solution isused, which contains about three pounds of the sulphate to one gallon of water. The efficiency of the solution may be increased by the use of other salts to reduce the resistance of the bath. One mixture found suit-able is as follows:

Ferrous ammonium sulphate, to saturation, about three lbs. Solution D Water 1 'gallon Magnesium sulphate 20 oz.

For use, equal volumes of solutions A, B, C and D are mixed together in an iron container which serves as an anode and the article to be coated is dipped in the solution and used as a cathode. Preferably, the current is kept at approximately 6 :volts and at a current density often to twelve amperes per square foot of the surface of the object to be coated.

The length of time the article is subjected Application filed November 2, 1928. Serial No. 316,883.

to this coating operation may vary within wide limits. For some purposes a mere flash 1s sufficient while for other purposes a coating of substantial thickness is desirable. Or-.

dinarily,- three to ten minutes suflices to produce the desired coating.

Electrolytically deposited iron rusts very easily and therefore it is preferable to subject the article to a phosphate bath as promptly as feasible after the deposition of 'the iron. This phosphate bath maybe prepared in any of the ways well known to the art and need not be specifically described here.

One suitable bath is described indetail in a patent on rustproofing issued to Green et' al., December 6, 1927, No. 1,651,694.

The time of reaction necessary to produce the insoluble phosphate coating is much less with theelectrolytically deposited iron than been cleaned by picklingfsince the phosphate solution ordinarily reacts very slowly with a pickled surface. 7

The advantage of the electrolytically deposited iron coating on an iron or steel article flows from the more prompt reaction of the electrolytically deposited iron. This makes possible a greater production with the same equipment and results in a more even and satisfactory coating. there is some wasteful hydrolytic dissociation resulting in the forming of sludge in the phosphate bath, aside from the reactions involved in the actual rust-proofing, and therefore the lessening of the time of reaction not only results in more production for the same amount of equipment and a more satisfactory coating on the articles, but also reduces the relative amount of waste in the bath.

Furthermore, it is sometimes desirable to place an insoluble phosphate coatin upon materials other than iron and upon a1 oys of iron or steel which do not react readily and uniformly with the regular phosphate rustprooling bath. All such articles which are susceptible to taking a coating of electrolytically deposited iron may be thus coated and then subjected to the phosphate bath, where- Furthe'rmore,

with the ordinary iron or steel surface. This is particularly true where the article has upon the electrolytically deposited iron reacts with the bath and produces the desired phosphate coating.

The insoluble phosphate coating referred to above forms a very good surface for receiving paint, varnish, lacquer or enamel. For this purpose a very thin coating of electrolytically deposited iron and a very brief treatment in the bath, sufficient to react with this iron, forms a satisfactory paint-receiving surface upon the material. Aluminum and zinc may be mentioned as common materials whose regular surface is not good for retaining paint or similar coatings, but which may be quickly and effectivel Y repared for painting by the above described method.

When treating articles havin surfaces of iron or steel, the electrolytical y deposited iron ma be utilized for initiating the deposition o the phosphate coating and the formation of this coating may be continued with the metal of the body of the article, and this is true of other metals such as zinc, manganese and magnesium, which will react with the bath to form insoluble phosphates. In any instance the treatment with the phosphate bath may be stopped short of the transformation of all of the electrolytically deposited iron into phosphates. However, since the electrolytically deposited iron reacts in the phosphate bath more promptly than any other material which I havejound, it is preferable to deposit substantially enough of this iron to carry out the reaction. Furthermore, if any of the electrolytically deposited iron is not acted upon by the phosphate bath, it constitutes a layer of material with different electrical characteristics and thereby increases galvanic action and liability to rusting. For this reason it is preferable to deposit substantially as much iron as will react in the phosphate bath and to continue the treatment in the phosphate bath until reaction with substantially all of the iron thus deposited has been completed.

In the usual phosphate rust-proofing bath the reactions result in the liberation of hydrogen at the surface of the work and this liberation of h drogen may be talren as an indication of t e reaction taking place. It is customary in the usual treatment of iron articles to continue boiling them in the hosphate solution as long as substantia reaction is indicated by the giving off of hydrogen. This gradually decreases as the coating becomes thicker, until finally it practically ceases, which indicates the conclusion of the operation.

When treating articles'coated with electrolytically deposited iron, the reaction and consequent giving oif of hydrogen is comparatively rapid as long as the reaction is with the electrolytically deposited iron, if this deposit is not so great as to carry the reaction to a conclusion. For preparing surfaces for painting, it is unnecessary to have a coating as thick as will be produced by carrying the reaction to a conclusion. Therefore, for preparing surfaces for painting, a comparatively thin deposit of iron may be produced electrolytically. When such a surface is treated by the phosphate solution, reaction takes place quite rapidly until the surface coating of iron has entered into the reaction, whereupon there is a marked decrease in the rate of reaction. This decrease may be taken to indicate the time when the phosphate solution has completed its reaction with the electrolytically deposited iron.

It will be readily understood that while one solution, together with current densities for the deposition of the iron coating, has been stated specifically, that any equivalent methodof electrolytically depositing the iron may be adopted. It will likewise be apparent that the method is applicable to any surface on which iron can be electrolytically deposited and where a coating of insoluble phosphates is desirable.

Zinc, magnesium or manganese, may be electrolytically deposited instead of iron, and form the coating which reacts with the phosphate solution to form a coating of insoluble phosphates; but iron reacts more promptly than zinc or magnesium, and is readily deposited electrolytically, and therefore is considered the best metal to use.

\Vhat I claim is:

1. The method which consists in electrolytically depositing a coating of iron upon the surface of an article and treating the iron thus deposited with a solution of phosphates until a coating of insoluble hosphates is formed upon the surface 0 article.

2. The process which consists in electrol tically depositing a coating of iron upon the surface of an article and treating the surface thus prepared by a dilute phosphate so lution until substantially all of the lIOIl thus deposited has reacted with the phosphate solution to form a coating of insoluble phosphates on the article.

3. The method which consists in electrolytically depositing upon the surface of an article a coating of Illt' i, treating the iron with a solution of phosphates until there is formed a coating of insoluble phosphates, and applying to the surface thus formed an adherent air-proof coating.

4. The method which consists in electrolytically depositing upon the surface of an article a coating of a. metal capable of reacting with a hosphate solution to form a coating of inso uble phosphates, and treating the coated article with a phosphate solution until substantially all of the electrolytically deposited metal has reacted with the solution.

5. The method of coating an iron or steel the l article which consists in electrolytically depositing an iron coating upon the surface of the iron or steel article, and treating the iron thus deposited with a solution of phosphates until a coating of insoluble phosphates is formed upon the surface thereof.

6. The method of coating an iron or steel article which consists in electrolytically depositing a coating of iron on the surface of the article, and treating the surface thus prepared by a phosphate solution until substantially all of the iron electrolytically deposited has reacted with the phosphate solution to form a coating of insoluble phosphates on the article.

7. The method of coating a surface of metal which does not react with a dilute phosphate bath to form a coating of insoluble phosphates, which consists in electrolytically depositing on said surface a coating of a metal capable of reacting with a dilute phosphate bath to form insoluble phosphate, and treating said coating with a dilute phosphate solution until there is formed a coating of insoluble phosphate.

8. The method of coating a surface of aluminum, which consists in electrolytically depositing thereon a coating of iron and treating the iron coating With a dilute phosphate bath until a coating of insoluble phosphate is formed.

9. The method of coating a surface of aluminum, which consists in electrolytically depositing thereon a coating of iron and treating the iron coating with a dilute phosphate bath until substantially all of the iron has reacted to form plies hates.

In testimony whereo I have hereunto signed my name to this specification.

ELMER M. JGNES. 

